Group 7 Flashcards
Observation during the reaction where br2 is produced
Brown solution SOLUTION is key
In terms of electrons state the meaning of the term oxidising agent
Causes another species to lose electrons but accepts electrons itself.
In sunlight chlorine can also oxidise water slowly to form oxygen. Write an equation for this reaction
2Cl2+2H2O—->4HCl+O2 or (4h+ +4cl- +o2)
Explain why chlorine has a lower bp than bromine
Chlorine is smaller than bromine so has fewer electrons (for my understanding less to create temp dipoles) the van der waals forces BETWEEN chlorine molecules are weaker. (Intermolecular forces)
Strontium carbonate reacts with nitric acid to produce a solution of strontium nitrate. Strontium sulfate does not react with nitric acid.
Describe briefly how you could obtain strontium sulfate from a mixture of strontium carbonate and strontium sulfate
Add nitric acid to the mixture until in excess and filter to isolate strontium sulfate.
Explain why drinking magnesium sulfate is effective in the treatment of barium poisoning
As insoluble barium sulfate is formed.
Medicines for the treatment of nervous disorders often contain calcium bromide. Silver nitrate acidified with dilute nitric acid can be used together with another reagent to test for the prescence of bromide ions in a solution of a med.
describe briefly how you would carry out this test and state observations.
Add silver nitrate and then dilute ammonia. Cream ppt and no visible change precip dissolves slightly in dilute ammonia.
Which of these substances reacts most rapidly to produce a silver halide ppt with acidified silver nitrate. (CH3Br, CH3Cl, CH3F, CH3I)
CH3I
How to separate and purify something
Filter off remaining ppt. Wash to remove soluble compounds. Dry to remove water.
A colourless solution contains a mixture of sodium chloride and sodium bromide.
develop a procedure to prepare a sample of pure silver bromide from this mixture.
Add silver nitrate to form precips pf agcl and agbr
Add excess dilute ammonia to ensure silver chloride dissolves.
Then filter off remaining solver bromide ppt wash to remove soluble compounds and dry to remove water.
Reaction between chlorine and cold dilute sodium hydroxide
Cl2+2HO- —> OCl-+Cl- + H2O
Other than cost, explain one advantage of using magnesium hydroxide rather than magnesium carbonate to reduce acidity in the stomach.
Does not produce co2 gas which distends stomach. Prevents burping
Explain why the precip of silver chloride was washed several times with deionised water
To remove soluble impurities
explian why the solution of strontium chloride was filtered to remove insoluble impurities before the addition of silver nitrate
as it would give an incorrect mass of AgCl
deduce reasons why the method of extraction from a low grade pre is a low cost process, do not include the cost of the ore
may use scrap metal, single step process, requires less energy
explain why chlorine is used to kill bacteria eventhough toxic
used in small amounts, health benefits outweigh the risks
what does chlorine do
dissolves in water to make a mixture of hcl and chloric acids. cl2+h20=hcl+hclo and cl2+h20=2h+ +cl- +clo-
what happens if you add an acid
more hydrogen ions are formed so the equibrium shifts to the left
what happens if you add an alkali, oh-
the ph increases so the equilibrium shifts to the right
test for chlorine
damp blue litmus paper, turns white. or pink to white over swimming pools
adding conc sulfuric acid to solid potassium chloride- write the simplest ionic equation and what species is responsible for the misty fumes produced
h2s04 + 2cl- –> 2hcl +so42-
and hcl
state the role of sulfuric acid and identify the yellow solid
oxidising agent and sulfur
give two features of a reaction at equilibrium
the conc of reac and products remains the same, adn the forward and backwards rate stay the same
state why the silver nitrate is acified when testing for iodide ions
it reacts with ions that would interfere with the test, for example carbonates
in terms of electrons state the meaning of a reducing agent
electron donor
state one risk in using hydrogen gas in metal extractikon
not flammable! explosive
major cost in the extraction of calcium via electrolysis
electricity
why is it not possible to measure the enthalpy change directly for areaction where co is made as a product
because co isnt the only product, co2 may also be formed if further oxidation occurs
state why the value quoted in c is the standard enthalpy of formation is the same as the one for carbon
because they both make a mole of co2, only from carbon and oxygen
When chlorine gas dissolves in cold water, a pale green solution is formed. In
this solution, the following equilibrium is established.
Cl2(g) + H2O(l) H+
(aq) + Cl–
(aq) + HClO(aq)
Give the formula of the species responsible for the pale green colour in the solution
of chlorine in water.
Use Le Chatelier’s principle to explain why the green colour disappears when
sodium hydroxide solution is added to this solution.
Cl2 (provides the pale green colour) M1 requires the formula M2 NaOH reacts with the acid(s)/the HCl/the HClO/H+ Ignore “reacts with the products” Ignore “reacts with chloride ion” Ignore “reacts with chlorine” M3 requires a correct answer in M2 Equilibrium shifts (from left ) to right OR wtte
state what is observed when silver nitrate solution is added to sodium fluoride solution
instead of saying no visible change, say colourless solution. allows nvc
the role of cl in nacl making hcl
hcl h - cl
proton acceptor or a base
give an equation for the redox reax between solid sodium bromide and conc sulfuric acid
normally nabr and h2so4 is the equation that makes nahso4 but thats not redox remember. the one after that is a redox so tweak it slightly
NaBr+ 2H2SO4 –>Na2So4 +Br2 +2H2O
the only thign that changed was the extra na added so instead form another so4 to get enough waters and also form na2so4
what halide can the scientist not idenitfy
fluoride as it is soluble so would dissolve
so no ppt would form
